<p> Atomic Structure Atom – smallest unit of matter Protons – positively charged; in nucleus Neutrons – neutrally charged (no charge); in nucleus Electrons – negatively charged; in energy levels around nucleus These particles are themselves made up of different combinations of the quark, an even smaller particle. Four Forces The nucleus (the positively-charged center of the atom) is held together by a strong nuclear force, which “glues” protons together. The electrons are attracted to the nucleus by an electromagnetic force. This holds the atom together. Gravity plays a part, too, but is the weakest of the forces in nature. There is also the weak force, which is responsible for radioactive decay.</p><p>Atomic Number = # of protons  The atomic number identifies the element  If the atomic number changes, the element changes  The number of protons will equal the number of electrons in a neutral atom; this is an atom without a charge</p><p>Atomic Mass Unit -- very small unit of mass used to measure subatomic particles</p><p>Mass Number = # of protons + # of neutrons  Elements can have different numbers of neutrons in their nuclei. These are called isotopes. Shorthand Notation: 14 C</p><p>Hyphen Notation: Carbon – 14</p><p>Determine the numbers of protons, neutrons, and electrons: 1.) 14 C</p><p>2.) Magnesium – 25</p><p>Write the isotope in shorthand notation: 1.) 7 protons, 8 neutrons, 7 electrons</p><p>2.) 21 neutrons, 20 electrons, 20 protons Bohr Model</p><p> Electrons reside in specific energy levels around the nucleus o 1st level: maximum of 2 electrons o 2nd level: maximum of 8 electrons o 3rd level: maximum of 18 electrons</p><p>Draw a Bohr model that has 8 protons, 7 neutrons, and 8 electrons.</p><p>Ions</p><p> Are formed when protons and electrons are not equal  Atom acquires a charge o the charge is positive if there are more protons than electrons o the charge is negative if there are more electrons than protons</p><p>Write in shorthand notation: 1.) 12 protons, 10 electrons, 13 neutrons</p><p>2.) 10 electrons, 9 protons, 9 neutrons</p><p>Determine numbers of protons, neutrons, electrons: 1.) 42 Sr +2</p><p>2.) 14 N -3</p>